Controlling the device performance by forming a stressed backside dielectric layer

ABSTRACT

A device includes a p-type metal-oxide-semiconductor (PMOS) device and an n-type metal-oxide-semiconductor (NMOS) device at a front surface of a semiconductor substrate. A first dielectric layer is disposed on a backside of the semiconductor substrate. The first dielectric layer applies a first stress of a first stress type to the semiconductor substrate, wherein the first dielectric layer is overlying the semiconductor substrate and overlapping a first one of the PMOS device and the NMOS device, and is not overlapping a second one of the PMOS device and the NMOS device. A second dielectric layer is disposed on the backside of the semiconductor substrate. The second dielectric layer applies a second stress to the semiconductor substrate, wherein the second stress is of a second stress type opposite to the first stress type. The second dielectric layer overlaps a second one of the PMOS device and the NMOS device.

This application is a divisional of U.S. patent application Ser. No.13/216,843, now U.S. Pat. No. 8,546,886, filed on Aug. 24, 2011,entitled “Controlling the Device Performance by Forming a StressedBackside Dielectric Layer,” which application is incorporated herein byreference in its entirety.

Since the invention of integrated circuits, the semiconductor industryhas experienced continuous rapid growth due to the constant improvementin the integration density of various electronic components (i.e.,transistors, diodes, resistors, capacitors, etc.). For the most part,this improvement in integration density has come from repeatedreductions in minimum feature size, allowing more components to beintegrated into a given chip area.

These integration improvements are essentially two-dimensional (2D) innature, in that the volume occupied by the integrated components isessentially on the surface of the semiconductor wafer. Although dramaticimprovements in lithography have resulted in considerable improvementsin 2D integrated circuit formation, there are physical limitations tothe density that can be achieved in two dimensions. One of theselimitations is the minimum size needed to make these components. Also,when more devices are put into one chip, more complex designs arerequired.

An additional limitation comes from the significant increase in thenumber and lengths of interconnections between devices as the number ofdevices increases. When the number and the lengths of interconnectionsincrease, both circuit RC delay and power consumption increase.

Among the efforts for resolving the above-discussed limitations,three-dimensional integrated circuit (3DIC) and stacked dies arecommonly used. Through-silicon vias (TSVs) are used in 3DIC and stackeddies. The related process steps are thus explored.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the embodiments, and the advantagesthereof, reference is now made to the following descriptions taken inconjunction with the accompanying drawings, in which:

FIGS. 1 through 7 are cross-sectional views of intermediate stages inthe manufacturing of a backside interconnect structure in accordancewith various embodiments;

FIGS. 8 through 10 illustrate cross-sectional views of dies comprisingbackside interconnect structures in accordance with alternativeembodiments; and

FIG. 11 illustrates the drift in saturation currents Idsat of PMOSdevices as a function of distances between the PMOS devices and TSVs.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the embodiments of the disclosure are discussedin detail below. It should be appreciated, however, that the embodimentsprovide many applicable inventive concepts that can be embodied in awide variety of specific contexts. The specific embodiments discussedare merely illustrative, and do not limit the scope of the disclosure.

A backside interconnect structure connected to through-substrate vias(TSVs, also sometimes referred to as through-silicon vias) and themethod of forming the same are provided. The intermediate stages in themanufacturing of an embodiment are illustrated. The variations of theembodiment are discussed. Throughout the various views and illustrativeembodiments, like reference numbers are used to designate like elements.

Referring to FIG. 1, chip 20, which includes substrate 10, is provided.Chip 20 is in wafer 100, which includes a plurality of chips identicalto chip 20. Substrate 10 may be a semiconductor substrate, such as abulk crystalline silicon substrate, although it may include othersemiconductor materials such as germanium, carbon, and the like.Substrate 10 may include n-well region 24 and p-well region 26 therein.Although one n-well region 24 and one p-well region 26 are shown in FIG.1, the illustrated n-well region 24 may represent all n-well regions inchip 20 (or wafer 100), and the illustrated p-well region 26 mayrepresent all p-well regions in chip 20 (or wafer 100). Alternatively,no p-well region is formed, and the corresponding n-typemetal-oxide-semiconductor (NMOS) devices 30 are formed directly onsubstrate 10, which may be of p-type.

Integrated circuit devices may be formed at front surface 10A ofsubstrate 10. The integrated circuit devices include p-typemetal-oxide-semiconductor (PMOS) device 28 and NMOS device 30.Similarly, although one PMOS device 28 and one NMOS device 30 are shownin FIG. 1, the illustrated PMOS device 28 may represent all PMOS devicesin chip 20 (or wafer 100), and the illustrated NMOS device 30 mayrepresent all NMOS devices in chip 20 (or wafer 100). Interconnectstructure 32, which includes metal lines and vias (not shown) formedtherein, is formed over substrate 10 and connected to the integratedcircuit devices such as PMOS device 28 and NMOS device 30. The metallines and vias may be formed of copper or copper alloys, and may beformed using damascene processes. Interconnect structure 32 may includeinter-layer dielectric (ILD) and inter-metal dielectrics (IMDs).

TSV 34 is formed in substrate 10, and extends from front surface 10A ofsubstrate 10 into substrate 10. Isolation layer 36 is formed on thesidewalls and at the bottom of TSV 34, and electrically insulates TSV 34from substrate 10. Isolation layer 36 may be formed of a dielectricmaterial such as silicon nitride, silicon oxide (for example,tetra-ethyl-ortho-silicate (TEOS) oxide), and the like.

Referring to FIG. 2, metal bump 40 is formed on the front side (the sidefacing up in FIG. 3) of, and protrudes beyond, the front surface of chip20. Wafer 100 is then mounted on carrier 46, for example, throughadhesive 48. In FIG. 3, a backside grinding is performed to removeexcess portion of substrate 10 from the backside of substrate 10, untilTSV 34 is exposed. An etch may be performed to further etch the backsurface of substrate 10, so that TSV 34 may protrude more out of backsurface 10B of substrate 10. Backside isolation layer 50 may be formedto cover back surface 10B of substrate 10. In an exemplary embodiment,the formation of backside isolation layer 50 includes blanket formingbackside isolation layer 50, and performing a light chemical mechanicalpolish (CMP) to remove the portion of backside isolation layer 50 thatis directly over TSV 34. Accordingly, TSV 34 is exposed through anopening in backside isolation layer 50. In alternative embodiments, theopening in backside isolation layer 50, through which TSV 34 is exposed,is formed by etching. Backside isolation layer 50 may be formed of acomposite layer including a silicon oxide layer and a silicon nitridelayer over the oxide layer, for example.

Referring to FIG. 4, seed layer 52, also referred to as an under-bumpmetallurgy (UBM), is blanket formed on backside isolation layer 50 andTSV 34. The usable materials of UBM 52 include copper or copper alloys.However, other metals such as titanium may be used. UBM 52 may also beformed of a composite layer comprising a titanium layer and a copperlayer over the titanium layer. In an embodiment, UBM 52 is formed usingsputtering.

FIG. 4 also illustrates the formation of mask 54. In an embodiment, mask54 is formed of photoresist. Alternatively, mask 54 is formed of a dryfilm. Mask 54 is then patterned to form opening 56 in mask 54, with TSV34 being directly under opening 56.

In FIG. 5, opening 56 is selectively filled with a metallic material,forming redistribution line (RDL) 58 in opening 56. In an embodiment,the filling material includes copper or copper alloys, although othermetals, such as nickel, solder, aluminum, gold, multi-layers thereof,and combinations thereof, may also be used. The filling methods mayinclude electro-chemical plating (ECP), electroless plating, or thelike. Mask 54 is then removed. As a result, the portions of UBM 52underlying mask 54 are exposed.

Referring to FIG. 6, the exposed portions of UBM 52 are removed byetching. The remaining RDL 58 may include RDL strip (also referred to asa redistribution trace) 52A that includes a portion directly over, andconnected to, TSV 34, and optionally RDL pad 58B joining RDL strip 52A.In FIG. 7 and subsequent figures, UBM 52 is not shown since it may beformed of similar materials as RDL 58, and thus becomes a part of RDL58.

Next, as shown in FIG. 7, passivation layer 60 is blanket formed andpatterned to form opening 64. Passivation layer 56 may be formed ofnitrides, oxides, and the like. A portion of RDL pad 58B is exposedthrough opening 64 in passivation layer 60. A center portion of RDL pad58B is exposed through opening 64, while the edge portions of RDL pad58B may be covered by passivation layer 60. RDL strip 52A may remain tobe covered by passivation layer 60.

Due to the formation of TSV 34, a stress is generated and applied tosubstrate 10 by TSV 34. The stress causes the performance of PMOS device28 and NMOS device 30 to drift as compared to if no TSV is formed insubstrate 10. FIG. 11 illustrates the experiment results revealing thedrift of the performance, wherein the experiment results are obtained byforming sample PMOS and NMOS devices and TSVs in first sample siliconwafers, and forming sample PMOS devices and NMOS devices on secondsample silicon wafers, with no TSV formed in the second sample siliconwafers. The saturation currents (Idsat) of the PMOS devices in the firstsample silicon wafers are compared to that of the PMOS devices in thesecond sample silicon wafers. The Y-axis represents the percentage ofthe drift in saturation currents Idsat of the PMOS devices in the firstsample silicon wafers, wherein the drift is calculated using thesaturation currents Idsat of the PMOS devices in the second samplesilicon wafers as criteria. The X-axis represents the distance of therespective PMOS devices from the TSVs. Referring to line 66, whenpassivation layer 60 is a uniform layer, the drift in saturationcurrents Idsat ranges from 6 percent to 24 percent (line 66).Furthermore, it is observed that the effect of the TSV to the drift isnot uniform, wherein the PMOS devices closer to the TSVs are affectedmore than the PMOS devices farther away from the TSVs. The non-uniformeffect causes difficulty in the prediction of device performance, anddifficulty in circuit design.

In an embodiment, passivation layer 60 is designed to have an inherentstress, and applies a stress to substrate 10. The performance of PMOSdevice 28 and NMOS device 30 are hence affected by the stress ofpassivation layer 60, and the performance drift of PMOS device 28 andNMOS device 30 may be reduced by adjusting the stress applied bypassivation layer 60. In an embodiment, passivation layer 60 may apply astress that compensates for the stress applied by TSVs, which means thatthe stress applied by passivation layer 60 neutralizes the stressapplied by the TSVs. For example, if TSV 34 applies a tensile stress tosubstrate 10, passivation layer 60 applies a compressive stress tosubstrate 10. Conversely, if TSV 34 applies a compressive stress tosubstrate 10, passivation layer 60 applies a tensile stress to substrate10. An equipment such as a Micro-Raman Spectrometer may be used tomeasure the stress applied to substrate 10 by TSV 34, and thenpassivation layer 60 may be formed to generate the stress that hassubstantially the same amplitude as, but has an inversed type than, thestress applied by TSV 34, so that the overall stress applied by TSV 34and passivation layer 60 may be a neutral stress (no stress). In thisembodiment, the neutral stress is also referred to as a target stress.In alternative embodiments, the stress generated by TSV 34 is measuredfrom sample wafers different from production wafers such as wafer 100.

In alternative embodiments, instead of compensating for the stresscaused by TSV, passivation layer 60 may also apply a stress that is ofthe same type as the stress generated by TSV 34. For example, if thestress applied to substrate 10 by TSV 34 is a tensile stress,passivation layer 60 also generates a tensile stress. Conversely, if thestress applied to substrate 10 by TSV 34 is a compressive stress,passivation layer 60 also generates a compressive stress. This maybenefit one of PMOS device 28 and NMOS device 30, so that it has agreater drive current. The other one of PMOS device 28 and MOS device 30is weakened. This embodiment may be used when one of PMOS device 28 andNMOS device needs to be improved in some applications.

Generally, in above-discussed embodiments, a desirable target stressapplied by TSV 34 and passivation layer 60 in combination ispre-determined. The stress applied by TSV 34 is measured (fromproduction wafers or sample wafers), and the difference between thepre-determined target stress and the stress applied by TSV 34 is made upby passivation layer 60. In the above-discussed embodiments, when thepre-determined target stress is a neutral stress (no stress), the stressapplied by passivation layer 60 will fully compensate for the stressapplied by TSV 34.

When using Micro-Raman Spectrometer or other equipment to measure thestress applied by TSV 34, the stress in substrate 10 may be measured ata selected location close to TSV 34, for example, with a distancebetween about 1 μm and about 10 μm from TSV 34, although differentdistances may be used. FIG. 7 schematically illustrate location 61, atwhich the desirable target stress is determined, and the stress appliedby TSV 34 is measured.

Referring to FIG. 11, line 68 illustrates experiment result obtainedfrom a sample wafer that includes passivation layer 60, which applies astress compensating for the stress generated by TSV 34. It is observedthat the performance drift, rather than ranging between about 6 percentand about 24 percent, only ranges between about −1 percent and about 3percent. In addition to the significant reduction in the performancedrift, it is also observed that the performance drift is more uniform,and for the distances (between the PMOS device and the TSVs) rangingfrom 2 μm and 8 μm, the difference in the performance drifts is onlyabout 4 percent. Accordingly, passivation 60 may globally make thestress more uniform throughout the entire wafer 100. In alternativeembodiments that the stresses applied by passivation layer 60strengthens (rather than compensates for) the stress applied by TSV, theperformance drifts of MOS devices are also more uniform.

The adjustment of the stress of passivation layer 60 may be achieved byselecting appropriate materials for passivation layer 60 and/oradjusting process conditions for depositing passivation layer 60. Forexample, in the embodiments wherein passivation layer 60 is formed ofsilicon nitride, the respective precursors may include silane andammonia, and the formation method may be plasma enhance chemical vapordeposition (PECVD) or other applicable deposition methods. In anembodiment, adjusting the UV curing dosage to be greater may cause thestress applied by passivation layer 60 to be more tensile, whileapplying Argon bombardment may cause the stress applied by passivationlayer 60 to be more compressive, and the stress of passivation layer 60may be adjusted into the desirable range.

FIGS. 8-10 illustrate cross-sectional views of chip 20 in accordancewith alternative embodiments. Unless specified otherwise, the referencenumerals in these embodiments represent like elements in the embodimentsillustrated in FIGS. 1 through 7. The initial steps of this embodimentare essentially the same as shown in FIGS. 1 through 6. Referring toFIG. 8, passivation layer 60, which is a composite layer, is formed.Passivation layer 60 includes sub-layer 60A and sub-layer 60B. In anembodiment, sub-layer 60A is formed overlying and vertically overlappingPMOS device 28 (which may represent substantially all PMOS devices inchip 20 or wafer 100), and may be formed overlying and verticallyoverlapping n-well region 24. Sub-layer 60A may not extend to overlyingand vertically overlapping substantially any of NMOS device 30 or P-wellregion 26 in chip 20 or wafer 100. Sub-layer 60B may extend overlyingand vertically overlapping substantially all PMOS devices 28 and NMOSdevices 30 in chip 20 or wafer 100, and overlying and verticallyoverlapping substantially all n-well regions 24 and p-well regions 26,except where RDL pads 58B are exposed. In an embodiment, sub-layer 60Aapplies a compressive stress to substrate 10, and sub-layer 60B appliesa tensile stress to substrate 10. Accordingly, the performance of NMOSdevice 30 is improved by passivation layer 60, while the performance ofPMOS device 28 is affected less due to the formation of sub-layer 60A.The formation of sub-layers 60A and 60B include blanket formingsub-layers 60A, patterning sub-layers 60A, and then forming sub-layers60B. The process conditions for forming sub-layers 60A and 60B may referto the embodiment shown in FIG. 7.

In alternative embodiments, as shown in FIG. 9, sub-layer 60A is formedoverlying and vertically overlapping NMOS device 30 (which may representsubstantially all NMOS devices in chip 20 or wafer 100), and may beformed overlying and vertically overlapping p-well region 26. Sub-layer60A may not extend to overlying and vertically overlapping any of PMOSdevices 28 and n-well regions 24 in chip 20 or wafer 100. Sub-layer 60Bmay extend overlying and vertically overlapping substantially all PMOSdevices 28 and NMOS devices 30, and overlying and vertically overlappingsubstantially all n-well regions 24 and p-well regions 26, except whereRDL pads 58B are exposed. In these embodiments, sub-layer 60A may applya tensile stress to substrate 10, and sub-layer 60B applies acompressive stress to substrate 10.

In yet other embodiments, as shown in FIG. 10, sub-layer 60A may beformed overlying and vertically overlapping NMOS device 30 (which mayrepresent substantially all NMOS devices in chip 20 or wafer 100), andmay be formed overlying and vertically overlapping p-well region 26.Sub-layer 60A may not extend to directly overlying and verticallyoverlapping PMOS device 28 and n-well region 24. Sub-layer 60B may beformed overlying and vertically overlapping PMOS device 28 (which mayrepresent substantially all PMOS devices in chip 20 or wafer 100), andmay be formed overlying and vertically overlapping n-well region 24.Sub-layer 60B may not extend to directly overlying and verticallyoverlapping NMOS device 30 and p-well region 26. In these embodiments,the target stress may be determined separately for PMOS devices and NMOSdevices based on the desirable performance of the PMOS and NMOS devices,and then the stresses that are to be provided by sub-layers 60A and 60Bare calculated, and sub-layers 60A and 60B are formed accordingly usingselected materials and process conditions to provide the desirabletarget stresses.

In the embodiments, dielectric layer(s) on the backside of semiconductorare formed to compensate for the stress applied to devices applied byTSVs, and/or to improve the performance of one of PMOS devices and NMOSdevices. The dielectric layer(s) may make the performance drift causedby TSVs more uniform.

In accordance with embodiments, a device includes a PMOS device and anNMOS device at a front surface of a semiconductor substrate. A firstdielectric layer is disposed on a backside of the semiconductorsubstrate. The first dielectric layer applies a first stress of a firststress type to the semiconductor substrate, wherein the first dielectriclayer is overlying the semiconductor substrate and verticallyoverlapping a first one of the PMOS device and the NMOS device, and isnot vertically overlapping a second one of the PMOS device and the NMOSdevice. A second dielectric layer is disposed on the backside of thesemiconductor substrate. The second dielectric layer applies a secondstress to the semiconductor substrate, wherein the second stress is of asecond stress type opposite to the first stress type. The seconddielectric layer vertically overlaps a second one of the PMOS device andthe NMOS device.

In accordance with other embodiments, a device includes a TSV extendingfrom a back surface of the semiconductor substrate down to a frontsurface of the semiconductor substrate. A metal pad is disposed on abackside of the semiconductor substrate and electrically coupled to theTSV. A first dielectric layer is over the back surface of thesemiconductor substrate, wherein the first dielectric layer applies afirst stress of a first stress type to the semiconductor substrate. Asecond dielectric layer is over and contacting the first dielectriclayer, wherein the second dielectric layer applies a second stress of asecond stress type opposite the first stress type to the semiconductorsubstrate. One of the first and the second dielectric layers includes aportion over and vertically overlapping an edge portion of the metalpad, with a center portion of the metal pad exposed through an openingin the one of the first and the second dielectric layers.

In accordance with yet other embodiments, a method includespre-determining a target stress at a selected location in asemiconductor substrate of a wafer, and forming a TSV in thesemiconductor substrate. A first stress applied to the selected locationby the TSV is found. A material and process conditions for forming adielectric layer that applies a second stress to the semiconductorsubstrate are selected, wherein at the selected location, a combinedstress of the first stress and a second stress is substantially equal tothe target stress. The dielectric layer is formed on a backside of thesemiconductor substrate using the material and the process conditions.

Although the embodiments and their advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the embodiments as defined by the appended claims. Moreover,the scope of the present application is not intended to be limited tothe particular embodiments of the process, machine, manufacture, andcomposition of matter, means, methods and steps described in thespecification. As one of ordinary skill in the art will readilyappreciate from the disclosure, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed, that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the disclosure.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps. In addition, each claim constitutes a separateembodiment, and the combination of various claims and embodiments arewithin the scope of the disclosure.

What is claimed is:
 1. A method comprising: pre-determining a targetstress at a selected location in a semiconductor substrate of a wafer;forming a through-substrate via (TSV) in the selected location; findinga first stress applied to the selected location by the TSV; selecting amaterial and process conditions for forming a dielectric layer thatapplies a second stress to the semiconductor substrate, wherein at theselected location, a combined stress of the first stress and a secondstress is substantially equal to the target stress; and forming thedielectric layer on a backside of the semiconductor substrate using thematerial and the process conditions.
 2. The method of claim 1, whereinthe target stress is a substantially neutral stress.
 3. The method ofclaim 1, wherein the forming the dielectric layer comprises: forming afirst sub-layer on the backside of the semiconductor substrate; removingthe first sub-layer from directly over substantially all p-typemetal-oxide-semiconductor (PMOS) devices or substantially all n-typemetal-oxide-semiconductor (NMOS) devices that are in the wafer; andforming a second sub-layer over remaining portions of the firstsub-layer, wherein the first and the second sub-layers apply stressesthat have opposite stress types to the semiconductor substrate.
 4. Themethod of claim 3, wherein the first and the second sub-layers areformed of substantially a same material, and wherein process conditionsfor forming the first sub-layer are different from process conditionsfor forming the second sub-layer.
 5. The method of claim 1, wherein thefinding the first stress comprises a step selected from the groupconsisting essentially of: measuring the first stress at the selectedlocation of the semiconductor substrate; and measuring the first stressfrom another sample wafer.
 6. The method of claim 1, wherein the targetstress is selected from the group consisting essentially of acompressive stress and a tensile stress.
 7. The method of claim 1,wherein the dielectric layer comprises a nitride.
 8. A methodcomprising: forming a through-substrate via (TSV) extending from a frontsurface of a semiconductor substrate of a wafer into the semiconductorsubstrate, wherein the wafer comprises a transistor at the front surfaceof the semiconductor substrate, wherein the semiconductor substratecomprises a back surface opposite to the front surface, and wherein theTSV applies a first stress to a nearby region of the semiconductorsubstrate, with the nearby region being adjacent to the TSV; performinga backside grinding on the back surface of the semiconductor substrateto expose the TSV; forming a backside isolation layer over andcontacting the back surface, wherein the TSV is exposed through thebackside isolation layer; forming a redistribution line on the backsideof the semiconductor substrate, wherein the redistribution line is overthe backside isolation layer; and forming a passivation layercomprising: a first portion over the redistribution line; a secondportion on sidewalls of the redistribution line; and a third portionlower than the first portion and the second portion, wherein thepassivation layer applies a second stress to the nearby region, with thesecond stress being of an opposite type than the first stress.
 9. Themethod of claim 8, wherein in the nearby region, the first stress issubstantially neutralized by the second stress.
 10. The method of claim8 further comprising: after the TSV is formed, measuring the firststress; and before the forming the passivation layer, selecting amaterial and process conditions for forming the passivation layer thatapplies the second stress to the nearby region.
 11. The method of claim10 further comprising: forming a sample wafer identical to the wafer;forming a sample TSV in the sample wafer; and after the sample TSV isformed on the sample wafer, measuring the first stress, wherein thefirst stress is equal to a stress applied by the sample TSV to thesample wafer.
 12. The method of claim 8, wherein the passivation layercomprises a nitride.
 13. A method comprising: forming athrough-substrate via (TSV) extending from a front surface of asemiconductor substrate of a wafer into the semiconductor substrate,wherein the wafer comprises a transistor at the front surface of thesemiconductor substrate, wherein the semiconductor substrate comprises aback surface opposite to the front surface, and wherein the TSV appliesa first stress to a nearby region of the semiconductor substrate, withthe nearby region being adjacent to the TSV; performing a backsidegrinding on the back surface of the semiconductor substrate to exposethe TSV; forming a backside isolation layer over and contacting the backsurface, wherein the TSV is exposed through the backside isolationlayer; forming a redistribution line on the backside of thesemiconductor substrate, wherein the redistribution line is over thebackside isolation layer; and forming a passivation layer comprising: afirst portion over the redistribution line; a second portion onsidewalls of the redistribution line; and a third portion lower than thefirst portion and the second portion, wherein the passivation layerapplies a second stress to the nearby region, with the second stressbeing of a same type as the first stress.
 14. The method of claim 13further comprising: after the TSV is formed, measuring the first stress;and before the forming the passivation layer, selecting a material andprocess conditions for forming the passivation layer that applies thesecond stress to the semiconductor substrate.
 15. The method of claim 13further comprising: forming a sample wafer identical to the wafer;forming a sample TSV in the sample wafer; and after the sample TSV isformed on the sample wafer, measuring the first stress, wherein thefirst stress is equal to a stress applied by the sample TSV to thesample wafer.
 16. The method of claim 13, wherein the step of formingthe passivation layer comprises: forming a first sub-layer; removing thefirst sub-layer from directly over substantially all p-typemetal-oxide-semiconductor (PMOS) devices or substantially all n-typemetal-oxide-semiconductor (NMOS) devices that are in the wafer; andforming a second sub-layer over remaining portions of the firstsub-layer.
 17. The method of claim 13, wherein the passivation layercomprises a nitride.